1. Field of the Invention
This invention relates to a meniscus lens having a refractive index distribution in the direction of the optic axis thereof.
2. Description of the Prior Art
In recent years, in various lens systems, the use of a refractive index distribution type lens having a refractive index distribution in a medium constituting the lens has been considered in order to reduce the number of component lenses and effect correction of aberrations. The index distribution type lenses are generally classified into a radial type lens having a refractive index distribution in the radial direction from the optic axis thereof, an axial type lens having a refractive index distribution in the direction of the optic axis thereof, and a spherical type lens comprising a combination of said two types. The axial type lens has an effect equal to that of a non-spherical surface and it is said that the contribution of the aberration coefficient thereof can be replaced with the contribution of the non-spherical surface. However, in spite of the fact that the axial type lens is easy to manufacture as compared with the radial type lens, the aberration correction effect of the axial type lens is smaller than that of the radial type lens, and there is known no example of the axial type lens in which attention is paid to the correction effect particularly for Petzval curvature of image field.